The prior art is described hereinafter with respect to a swash plate-type compressor, a resin-based coating layer covering the swash plate of a swash plate type compressor, a resin-based sliding material other than the one used for a swash plate-type compressor, spherical carbonaceous material, and then sliding properties of graphite.
Swash Plate Type Compressor
Existing variable-displacement swash plate-type compressors have a structure shown, for example, in FIG. 1. This drawing is from Patent Document No. 1: Japanese Unexamined Patent Publication (kokai) No. 2003-183685. The referential numerals in the drawing indicate the following parts or positions: 10—cylinder block; 12—cylinder bore; 14—single head piston; 16—front housing: 18—rear housing (suction port and supply port are not shown in the drawing); 20—valve plate (valve and port are not shown in the drawing); 21—housing; 22—suction chamber; 24—exhaustion chamber; 50—rotary shaft; 60—swash plate; 61—through hole; 62—rotary plate; 64—thrust bearing; 66—hinge mechanism; 67—arm; 68—guide aperture; 69—guide pin; 70—engagement; 72—head; 76—shoe; 80—guide aperture; 86—swash-plate chamber; 87—compression chamber; 90—schematically shown electro-magnetic valve; 100—exhaust channel; 102—supporting aperture.
Patent Document 1 describes the following operating mechanism of a variable-displacement swash plate-type compressor. An exhausting chamber 24, which is on the high pressure side, and a suction chamber 22, which is on the low pressure side, generate a pressure difference, which is utilized to regulate the pressure within a swash-plate chamber 86. The front and rear sides of a piston 14 are exposed to the pressure in a compression chamber 87 within a cylinder bore 12. The difference between this pressure and the pressure of the swash-plate chamber 86 is regulated to change the inclination angle of a swash plate 60. As a result, the stroke of the piston 14, and hence the exhausting volume of the compressor, is adjusted. Specifically, an electro-magnetic valve 90 is switched on or off to control the pressure in the swash-plate chamber 86, and, in turn, the swash-plate chamber 86 is communicated or disconnected with the exhaustion chamber 24.
FIG. 2 is an enlarged schematic view of essential parts of the swash plate-type compressor shown in FIG. 1. In FIG. 2, the shoe clearance between a shoe 76 and the swash plate 60 is denoted by 120. In an enlarged view of the shoe shown in FIG. 3, 76a denotes a flat plane; 76b, a spherical plane; and 76c, an abutting surface with a piston. The shoe 76 is a semi-spherical member typically manufactured through quenching SUJ2, followed by finishing. An intermediate layer is formed through thermal spraying, plating, or chemical conversion on the surface of a steel material, and resin-based surface treatment is applied via the intermediate layer on the top surface of the swash plate.
The shoe 76 is a sliding member located between the swash plate 60 and the piston 14, as is shown in FIGS. 2 and 3. Since the piston-facing surface of the shoe 76 is a spherical plane 76b, the shoe 76 is capable of oscillating depending upon the change in inclination angle of the swash plate. The rotating swash plate 60 is positioned aslant and oscillates with respect to the axial line of the compressor, while both surfaces of the swash plate 60 slide on the flat plane 76a of the shoe. Since the middle portion of the flat plane 76a of the shoe is slightly convex (not shown in the drawing), oil film is formed on this plane, thereby decreasing the friction resistance with respect to the swash plate 60.
Surface Treatment of Swash Plate by Resin-Based Sliding Material
According to the prior art, a sliding coating layer, which is based on polyimide or polyamide-imide, is provided on the swash plate of a swash plate-type compressor. Related prior art documents are: Patent Document 1—Japanese Unexamined Patent Publication (kokai) No. 2003-183685; Patent Document 2—Japanese Unexamined Patent Publication (kokai) No. 2000-265953; Patent Document 3—Japanese Unexamined Patent Publication (kokai) No. 2005-89514; and, Patent Document 4—WO02/075172A1.
The coating layer provided on the surface of a steel-based swash plate in Patent Document 1 is formed of solid lubricant, such as MoS2, PTFE, or graphite, such metallic powder of Ni, Fe, Mn, Cr or Mo having a particle diameter of 20 nm, and a polyamide-imide binder.
A liquid mixture of resin, such as polyamide-imide resin or polyimide resin and a metal or alloy powder having a particle size of 10 to 100 μm are baked on the surface of a swash plate to form a coating layer in Patent Document 2. The metal is for example Sn, Ag, Al, Cu, Zn, Ni, Si, Co, Ti, W, Mo, Mg or Fe. The alloy is of these metals.
In Patent Document 3, a solid lubricant is bonded to at least one binder selected from the group consisting of polyamide-imide, polyimide and epoxy resin. The solid lubricant contains 10 to 40 vol. % of molybdenum disulfide, 10 to 40 vol. % of flake-shaped graphite or scale-shaped graphite, and 1 to 40 vol. % of polytetrafluoroethylene. The total amount of the solid lubricants is 30 to 60 vol. %. In Patent Document 4, the following proposals are made. The swash plate of a swash-plate compressor is coated with a solid-lubricant coating layer produced from polyamide-imide resin and at least one of PTFE and graphite. In addition, concentric grooves and convexities between the neighboring grooves are provided on the sliding surface. It is described that synthetic graphite of high crystallization degree is preferred.
Non-Patent Documents: Tribologist Vol. 55, No. 9 (2010), pages 10-12 illustrates trends of a swash-plate compressor used for automotive air-conditioning. In a compressor in which an alternative fluorocarbon cooling medium HFC1113a is used, seizure is more likely to occur than in a compressor using a fluorocarbon cooling medium CFC12. Therefore, an intermediate layer formed of flame-sprayed copper-based material such as Cu—Pb and Cu—Si is provided on the iron-based swash plate in the variable-displacement type compressor, and the resin-based coating layer containing a solid lubricant is provided on the intermediate layer.
Sliding Material Used in Parts Other than Swash Plate of Swash Plate Compressor
Hitherto, a polyether-ether ketone-based resin bearing has been used as a bearing of a motor for information media such as a hard disc and DVD disc according to Patent Document 5: Japanese Unexamined Patent Publication (kokai) No. 2009-185103. This patent document proposes to replace the conventional motor bearing with a bearing, which contains (a) 100 parts by weight of a thermoplastic resin including polyarylene sulfide resin and aromatic polyamide-imide resin, (b) 1 to 50 parts by weight of such a spherical filler as a ceramic balloon, “sirasu” (a Japanese word) balloon, a glass balloon, a metallic balloon, ceramic particles, silica, glass beads, and metallic powder, and (c) 1 to 50 parts by weight of solid lubricant. It is described that scale-shaped graphite, nodular graphite, flat-sheet-shaped graphite and spherical graphite can be used, but scale-shaped graphite is preferred.
Spherical Carbonaceous Material
In Patent Document 6: Japanese Patent No. 3026269, the present applicant proposed a polyamide-imide resin-based sliding material containing 5 to 80% by weight of heat-treated and dispersed resin particles essentially individually isolated from each other. These particles are formed by heat treating and spheroidizing phenol resin.
Patent Document 7: Japanese Unexamined Patent Publication No. Hei 5-331314 proposes a heat-resistant resin sliding material composed of 40 to 95% by weight of a heat resistant resin such as polyimide resin, and 5 to 60% by weight of spherical graphite having an average particle diameter of 3 to 40 μm, which is obtained by calcining resin-based spherical particles in an inert-gas atmosphere or vacuum. The spherical graphite is described as follows. Preferably, the spherical graphite has a uniform particle diameter, an average-particle diameter of 3 to 40 μm, and geometrically highly spherical shape. Preferably, the starting material of the spherical graphite is at least one of phenol resin, naphthalene resin, furan resin, xylene resin, divinylbenzene polymer, and styrene-divynilbenzene copolymer. A method for producing such spherical graphite comprises subjecting these starting materials to known emulsion polymerization to produce spherical particles, and calcining the resultant spherical particles in an inert gas protective atmosphere or vacuum, thereby carbonizing and/or graphitizing the same.
Spherical carbon particles disclosed in Patent Document 8: Japanese Unexamined Patent Publication (kokai) Hei 7-223809 has a highly oriented, quasi-graphite crystal structure. These spherical fine graphite particles are isotropic. Various resins in which spherical carbon particles are dispersed can be used as the sliding member. These fine carbon particles are meso phase microbeads (mesocarbon microbeads), coal tar, coal tar pitch, asphalt and the like, which are heat-treated at 350 to 450 degrees C. to yield spherical crystals. They are separated from coal tar and the like and is then finely divided, followed by graphitization at 1500 to 3000 degrees C. During this process, spheroidization proceeds according to the description. However, the meso phase microbeads shown in the microscope photograph of that publication are considerably deformed from the geometrically spherical shape.
Sliding Properties of Graphite
    (a) Graphite is a material having a laminar crystal structure, in which (002) planes are superimposed. Slip is likely to occur between these planes. This property is utilized to realize the low-friction property.    (b) Graphite having a higher degree of graphitization is closer to natural graphite. Such graphite is soft and well lubricating. Graphite having a lower degree of graphitization is hard carbon. A hard carbon-particle additive is used to improve wear resistance and to control friction. Meanwhile, high degree of graphitization and improved lubricating property of flake-shaped graphite is believed to be utilized in Patent Document No. 3. The spherical graphite having highly near-sphere shape proposed in Patent Documents Nos. 6 and 7 is believed to be hard carbon.